The self-serve tools, specifically cancel.py has received some important usability upgrades at the urging of jst and ehsan. Now, simply running

python cancel.py

will be enough to get you going – you’ll be prompted for your username, password, branch and hg revision. The builds displayed also show their state (running, pending or complete) as well, so it’s easier to find what you’re looking for. Let me know if there are more changes you’d like made!